A) Field of the Invention
The present invention relates to a biconvex rod-lens for the optics assemblies of medical or technical endoscopes, and a rod-lens comprising a fluid encapsulated between two correcting lenses, the external surfaces of which are convex in shape and, more particularly, to an inexpensive and durable image transmission optical system to be used with an inflexible-type endoscope or the like, which is arranged to transmit an image by using a plural number of relay lenses.
B) Description of the Prior Art
An inflexible-type endoscope 1 illustrated in FIG. 1 consists of an eyepiece 2 to the distal end of which is affixed a connector 7a for attachment of a fiber optics light delivery assembly (not shown) and a tubular outer shaft 3 receiving the optical elements of the assembly. The said optical elements, shown in FIG. 1A, consist of the objective 8 which is arranged near the distal end of shaft 3, and a series of lenses 9 arranged to transmit an image from the proximal end of objective 8 to the distal portion of eyepiece 2.
According to the prior art, as illustrated in FIG. 2, an image transmission optical system consists of two rod-like cemented doublets 9, each consisting of the biconvex positive lens element 12 made, for example, from a crown glass and the concavo-convex negative lens element 14 cemented to lens 12, and being made, for example, from a flint glass. Said image transmitting optical system is arranged so that the convex surfaces of the negative lens elements 14 thereof face each other in opposition, said assemblies embraced in a thin-walled inner tube 10 within the outer shaft 3 in an eccentric and interlocking relationship. The said rod-like cemented doublets 9 are held in longitudinally spaced relationship by means of thin-walled tubular spacers 11. The shaft 3 and inner tube 10 cooperate to define a space which has a crescent-shaped cross section and in which are arranged fiber optics light guides 7 for transmitting light fed through connector 7a, to the distal end of endoscope assembly 1.
The rod-like lens 9, an enlarged view of which is shown as FIG. 3, is hereinbefore described as a cemented doublet purely on the basis that such nomenclature is a suitable matrix for optical design purposes. The positive lens 12 of a cemented doublet 9, however, is not amenable to low cost, volume manufacturing. Accordingly, it has become customary and prudent to divide positive lens 12 of rod-like lens 9 into three parts, to wit, plano-convex lens 12a, plano-plano lens 12b, and plano-convex lens 12c, so that said lenses can be economically and simultaneously processed as individual parts in multiples.
Once fabricated, the individual lenses are subsequently joined as a cemented assemblage comprising lens 12a, lens 12b, and lens 12c which is equivalent in form and function to monolithic rod lens 12. Said lens assembly, as shown in FIG. 4, is cemented to negative lens 14 to form a quadruplet lens assembly 13 which is equivalent in form and function to doublet 9. It should also be mentioned in passing that the fractionation process of rod-like lens 12 has its limits. Typically, there is economic justification for dividing the rod-like lens 12 into three or fewer pieces; however, should the rod-like lens 12 be required to be processed in four or more pieces, the cost of assembly outweighs the potential savings afforded by fabricating the lenses in multiples.
In its clinical application, the endoscope 1 is inserted into a human subject by grasping it by its proximal end, manipulating its distal end of shaft 3 through a natural or incised aperture, into the interior of a viscera. Such procedure may inadvertently cause the outer tube 3 to be deformed or bent at its approximate mid-length, the extent of which depending on the anatomy of the viscera, the force applied and the modulus of elasticity of the outer tube 3. As a concomitant result of the bending of outer tube 3, inner tube 10 is subjected to not only bending forces but also to compressive forces. Due to the small diameter and considerable length of the rod-like lens 9 and given that it is in a close tolerance embrace with inner tube 10, said lenses are prone to fracture when inner tube 10 is otherwise compressed and bent, especially at the cemented joints.
There is known an image transmitting optical system having a composition as illustrated in FIG. 5. Said known image transmitting optical system is composed of rod-like lens assembly 13, in which the mechanical diameter at the middle of the rod lens is less than the outer diameter at its ends, thus providing clearance between the mid-portion of the rod-like lens and inner tube 10. Rod lenses so shaped are supported in the inner tube 10 merely at their end regions, so that the lens assembly 13 is purported to be protected from fracture or breakage at the cemented joints when the inner tube 10 is bent.
There is known another image transmitting optical system having a composition as illustrated in FIG. 6. Said image transmitting optical system is composed of rod-like lens assembly 13, in which there is present at least one cylindrical collar of greater diameter than the adjacent lengths of each of the rods. Rod lenses so shaped are supported in their inner tube 10 only by way of the said collars, thus providing clearance between the rod-like lens and the inner tube 10 at the regions adjacent to the cylindrical collars and therefore purporting to protect the cemented joint from stress and possible fracture when the inner tube 10 is bent.
The aforementioned known methods of eliminating the possibilities for stress fractures of the rod lenses in image transmitting optical systems have, nevertheless, several significant drawbacks.
First and foremost, there remains, despite the aforementioned precautions, the distinct possibility that the cemented joints located at either ends of the rod-like lenses may be subjected to shear stress sufficient for risk of fracture. This is simply the result of the aforementioned mounting constraints existing at one end portion or both end portions of the rod-like lens assembly where one or more cemented joints may be located. Second, the economy of manufacture is impacted by the additional requirements of edging and centering the rod-like lens assembly which does not exhibit a uniform diameter along its length. Third, by constraining the diameter of the rod-like lenses of the image transmitting optical system for the purpose of eliminating stress fractures when the inner tube 10 is bent, an unnecessarily restrictive aperture stop and/or field stop my be created which places an upper limit upon the maximum value to which the image diameter, numerical aperture, or both, may reach. Consequently, this may have an unfavorable effect upon the luminous energy throughput or etendue of the image transmitting optical system.
Thus, a need has arisen for an image transmitting optical system which is inexpensive, durable and energetically efficient relative to known image transmitting optical systems. This need is pronounced when it is desired to utilize the said image transmitting optical system in an inflexible-type endoscope.